107 lines
2.8 KiB
C++
107 lines
2.8 KiB
C++
//
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// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2018
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#pragma once
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#include "td/utils/common.h"
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#include "td/utils/port/thread.h"
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#include <atomic>
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#include <condition_variable>
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#include <mutex>
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namespace td {
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class MpmcWaiter {
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public:
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int wait(int yields, uint32 worker_id) {
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if (yields < RoundsTillSleepy) {
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td::this_thread::yield();
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return yields + 1;
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} else if (yields == RoundsTillSleepy) {
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auto state = state_.load(std::memory_order_relaxed);
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if (!State::has_worker(state)) {
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auto new_state = State::with_worker(state, worker_id);
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if (state_.compare_exchange_strong(state, new_state)) {
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td::this_thread::yield();
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return yields + 1;
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}
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if (state == State::awake()) {
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return 0;
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}
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}
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td::this_thread::yield();
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return 0;
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} else if (yields < RoundsTillAsleep) {
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auto state = state_.load(std::memory_order_acquire);
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if (State::still_sleepy(state, worker_id)) {
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td::this_thread::yield();
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return yields + 1;
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}
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return 0;
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} else {
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auto state = state_.load(std::memory_order_acquire);
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if (State::still_sleepy(state, worker_id)) {
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std::unique_lock<std::mutex> lock(mutex_);
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if (state_.compare_exchange_strong(state, State::asleep(), std::memory_order_acq_rel)) {
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condition_variable_.wait(lock);
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}
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}
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return 0;
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}
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}
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int stop_wait(int yields, uint32 worker_id) {
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if (yields > RoundsTillSleepy) {
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notify_cold();
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}
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return 0;
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}
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void notify() {
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if (state_.load(std::memory_order_acquire) == State::awake()) {
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return;
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}
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notify_cold();
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}
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private:
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struct State {
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static constexpr uint32 awake() {
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return 0;
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}
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static constexpr uint32 asleep() {
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return 1;
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}
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static bool is_asleep(uint32 state) {
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return (state & 1) != 0;
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}
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static bool has_worker(uint32 state) {
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return (state >> 1) != 0;
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}
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static int32 with_worker(uint32 state, uint32 worker) {
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return state | ((worker + 1) << 1);
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}
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static bool still_sleepy(uint32 state, uint32 worker) {
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return (state >> 1) == (worker + 1);
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}
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};
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enum { RoundsTillSleepy = 32, RoundsTillAsleep = 64 };
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std::atomic<uint32> state_{State::awake()};
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std::mutex mutex_;
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std::condition_variable condition_variable_;
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void notify_cold() {
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auto old_state = state_.exchange(State::awake(), std::memory_order_release);
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if (State::is_asleep(old_state)) {
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std::lock_guard<std::mutex> guard(mutex_);
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condition_variable_.notify_all();
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}
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}
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};
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} // namespace td
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